doc: Add a small paragraph to activate shell completion

docs/cli.rst

@@ -9,6 +9,38 @@ Shared command-line interface
 .. click:: swh.core.cli:swh
   :prog: swh
 
+Shell Completion
+----------------
+
+You may activate the command line completion mechanism for your shell. The
+`swh` tool is using the `click`_ package, so activating command completion is a
+simple matter of:
+
+.. tab-set::
+
+   .. tab-item:: Bash
+
+      Add this to your `.bashrc`
+
+      .. code-block:: bash
+
+         eval "$(_SWH_COMPLETE=bash_source swh)"
+
+   .. tab-item:: Zsh
+
+      Add this to your `.zshrc`
+
+      .. code-block:: zsh
+
+         eval "$(_SWH_COMPLETE=zsh_source swh)"
+
+
+See `click documentation`_ for more details and options.
+
+.. _`click`: https://click.palletsprojects.com
+.. _`click documentation`: https://click.palletsprojects.com/en/8.1.x/shell-completion
+
+
 Database initialization utilities
 ---------------------------------